Eddie Hearn was warned Anthony Joshua to "snap out of it" ahead of his rematch with Andy Ruiz Jr.
Joshua has admitted to being disillusioned with the sport having lost his three heavyweight world titles in June.
He has however triggered the rematch clause in his contract and will challenge Ruiz on December 7 in Saudi Arabia.
And his promoter told Sky Sports: "I think he's just got to snap out of it."
"I think he was disillusioned with the sport because he wanted to fight Deontay Wilder .
"He couldn't get that fight and as he said in the interview, he didn't really want to fight Andy Ruiz. But tough, you fought him and you fought a real hungry guy.
"I think the great thing about this promotion is that now, for the first time next week, he looks a man in the eyes who is the only man to beat him as a professional.
"It's going to be absolutely huge. The whole world will stop to watch this fight."
Joshua appeared too relaxed before his first meeting with Ruiz, allowing his challenger to pose with his belts beforehand.
Conspiracy theories have raged since that night at Madison Square Garden with suggestions Joshua was not motivated.
But Hearn insists the dethroned champion has his hunger back ahead of the rematch.
'He doesn't even want to talk to him, he wants to knock him clean out," he added.
"He didn't have that feeling last time but it's a new game now, a new game. Josh wants to take his head off.
